1. Field of the Invention
The present invention relates to a dielectric filter and a dielectric duplexer each including plural inner conductors inside of a dielectric block, and an outer conductor on the outside of the dielectric block, and input-output electrodes which are capacitance-coupled to the predetermined inner conductors, respectively, and a communication apparatus using them.
2. Related Art
A conventional dielectric filter having plural resonator holes formed inside of a dielectric block has such a structure as shown in FIG. 8. In the figures shown below, the dot-shaded portion is the portion of the dielectric block which is visible.
In FIG. 8, the reference numeral 1 designates a dielectric block having a rectangular parallelepiped shape, in which three resonator holes 2a, 2b, and 2c are formed to elongate from one of the end-faces to the other end-face, and inner conductors 3a, 3b, and 3c are formed on the inner walls, respectively. An outer conductor 4 is formed on the outside (five faces) of the dielectric block 1 excluding the one end-side. In particular, the inner conductors 3a through 3c are separated from the outer conductor 4 in the one end-face so that the one end-face becomes an open end-face, and in the other end-face, are connected to the outer conductor 4 so that the end-face becomes a short-circuiting face. In the open end-face, coupling electrodes 5a, 5b, and 5c connected to the inner conductors 3a, 3b, and 3c, correspondingly, are formed, and input-output electrodes 6a and 6b are formed. The input-output electrodes 6a and 6b are formed adjacently to the coupling electrodes 5a and 5c lying oppositely. The input-output electrodes 6a and 6b are formed to extend onto one side (the upper side in FIG. 8) of the dielectric block 1 which is a mounting face. Outer conductor non-forming portions are provided so as to surround the input-output electrodes 6a and 6b, which are caused to separate from the outer conductor 4.
The dielectric filter comprises the three resonator stages which correspond to the inner conductors 3a through 3c. The respective resonators are coupled through capacitances produced between the coupling electrodes 5a, 5b, and 5c, and between the coupling electrodes 5a, 5b, and 5c and the outer conductor 4, and an external coupling is attained through an external coupling capacitance Ce produced between the input-output electrodes 6a and 6b and the corresponding coupling electrodes 5a and 5c. 
However, in the above-described conventional dielectric filter, since the input-output electrodes are formed also on the mounting face (side) of the dielectric block, the result is deterioration of the Q0 of the resonator, so that the filter characteristics (insertion loss and attenuation characteristics) are damaged. This is because the lower the proportion of the outer sides of the dielectric block covered by the outer conductor, the more the Q0 is deteriorated. Especially, when the axial length (the length of the dielectric block) of the resonators is shorter with the use of higher frequencies, this Q0 deterioration is even worse.
To solve the above-described problems, a preferred embodiment of the present invention provides a dielectric filter and a dielectric duplexer each of which has good characteristics without the Q0 being deteriorated, and can be surface-mounted steadily and securely, and a communication apparatus using the same.
One preferred embodiment according to the present invention provides a dielectric filter and a dielectric duplexer each of which comprises a dielectric block in a substantially rectangular parallelepiped shape, having one pair of opposite end-faces and plural sides extending between the paired opposite end-faces, one of the plural sides being a mounting face; plural resonator holes elongating through the inside of the dielectric block across the paired opposite end faces; inner conductors provided on the inner walls of the plural resonator holes, correspondingly; an outer conductor provided on the outside of the dielectric block; input-output electrodes each provided only on one of the paired opposite end-faces, separated from the outer conductor, and capacitance-coupled to the predetermined inner conductors, respectively; and conductive terminals for external connection, connected to the input-output electrodes, having at least a part thereof lying substantially in the same plane as the mounting face.
The other preferred embodiment according to the present invention provide a dielectric filter and a dielectric duplexer each of which comprises a dielectric block in a substantially rectangular parallelepiped shape, having a pair of opposite end-faces and plural sides extending between the paired opposite end-faces, one of the plural sides being a mounting face; plural resonator holes elongating through the inside of the dielectric block across the paired opposite end-faces; inner conductors provided on the inner walls of the plural resonator holes, correspondingly; an outer conductor provided on the outside of the dielectric block; a beveling portion formed in the edge portion between the one of the paired opposite end-faces and the mounting face; and input-output electrodes formed to extend over the one of the paired opposite end-faces and the beveling portion, separated from the outer conductor, and capacitance-coupled to the inner conductors, correspondingly.
In the dielectric filter and the dielectric duplexer each having the above-described configuration, since the input-output electrodes are formed only on the end-face of the dielectric block or are formed to extend over the end-face and the beveling portion, the deterioration of Q0, caused by the input-output electrodes, is reduced. That is, the deterioration of Q0 is decreased, as compared with that caused by the input-output electrodes formed on the mounting face (the side) of the dielectric block as described in the conventional example. Further, with the conductive terminals connected to the input-output electrodes and the input-output electrodes formed to extend over the end-face and the beveling portion, surface-mounting on a circuit board can be achieved steadily and securely.
Further, by excluding the outer conductor on the mounting face in the vicinity of the input-output electrodes, short-circuiting between the input-output electrodes and the conductive terminals, and the outer conductor, caused by solder or the like applied at mounting, can be prevented.
Further, the communication apparatus of the present invention, since it is configured, including the dielectric filter or the dielectric duplexer having the above-described features, has improved characteristics.
Hereinafter, an embodiment of the dielectric filter according to the present invention will be described with reference to the attached drawings, in which like references denote like elements and parts.